Pretrial discussions began on Wednesday in a rare public interest lawsuit whose plaintiffs include non-governmental environmental organizations.

The three plaintiffs �� Friend of Nature, Chongqing Green Volunteers Union and the Qujing environmental protection bureau �� exchanged evidence with Luliang Chemical Industry, the defendant, on Wednesday, said Chang Cheng, a program officer of Friend of Nature.

The exchange and discussion will last at least three days, Chang said.

The process is regarded as the prelude to the trial of the case, a "landmark and probably the first" public interest environmental litigation filed by NGOs, Chang said.

Luliang Chemical Industry is accused of discharging more than 5,000 metric tons of highly toxic heavy metal in three townships of Qujing, in Southwest China's Yunnan province, in 2011.

The company did not comment on the case on Wednesday.

The intermediate people's court of the city, which set up an environmental tribunal in 2008, accepted the case in October.

"We collected a lot of evidence about the case, hoping to have enough preparation before the formal trial begins," Chang said.

Zeng Xiangbin, a lawyer representing Friend of Nature, said the court will investigate the authenticity of the evidence before it formally hears the case.

Yang Shuxian, director of Qujing city environmental protection bureau, said he is confident of winning the case and hoped to minimize the pollution caused by the plant.

"We've been checking the chromium-contaminated waste since the case happened and believe the work can be finished at end of this year," he said.

"The plant is closed and the environment around us is better now," said Wang Xiaohong, a resident of Xinglong village near the pollution source. "I'm waiting for good news in the case and hope our living area won't be polluted in the future."

Zeng, of the Ying Ke Law Firm branch in Wuhan, Hubei province, said the plaintiffs demand the chemical factory pay 10 million yuan ($1.58 million) in compensation, and the money can be used to establish a fund to restore the environment under the supervision of the court, the plant and other independent environmental organizations.

The case is one of the few to have been co-filed by NGOs.

According to the Civil Procedure Law, social groups without government background cannot independently file public interest litigation on environment.

"The definition of the social group that is eligible to sue pollutants on behalf of the public is too narrow," said Zhao Hongmei, an associate professor at China University of Political Science and Law.

In this case, the court accepted the case filed by Friend of Nature and Chongqing Green Volunteers Union because they did so together with the local government, Zhao said.

Bie Tao, deputy director of the Ministry of Environmental Protection's policies, laws and regulations department, has suggested lawmakers broaden the definition of social group and give more room for NGOs to launch public interest litigation.

"The legislators should be open-minded toward such organizations that have professional knowledge and will work well to protect the public interest," he said.

Other problems hindering NGOs from launching environmental cases included the lack of the judicial expertise to evaluate the environment damage, Chang from Friend of Nature said.

"Without the expertise, it is be hard to define the change to the environment," he said. "The expense of environmental evaluation is very large, which a small organization cannot afford."

In addition, supervising the use of defendants' compensation and public funds is also a challenge in public interest litigations, he said.